El Niño

Stu Ostro
Stu Ostro
Jan 8, 2016 · 7 min read
© Michael Cavna and United Feature Syndicate; reproduced with permission

The cartoon and classic SNL skit have an underlying seriousness to them, engendered by the hype during the last exceptionally strong El Niño in 1997–98.

And now, with the viral information age in which we live, we have Godzilla! (Though did you know that the scientist from whom that originated for this El Niño previously called two past El Niños the same thing, and once even referred to a Godzilla Santa Ana wind event?)

El Niño is an influence upon weather but it is also a phenomenon that is often misunderstood, and a term that lends itself to misuse and sensationalism. As in recent days, when it’s gotten out of control.

I am an operational meteorologist and weather forecaster, and not an El Niño expert; what follows is what I’ve learned based on that experience during the course of more than 10 El Niños since the late 1970s when I started forecasting, along with information from those whose careers have been focused on the phenomenon and from peer-reviewed research on the topic. This can serve as both a scientific primer and a journalistic guide.

Myths — what El Niño is *not*

  • A weather event. A flood. A rainbow. A storm. El Niño can influence storms and patterns, but there are not “El Niño storms” per se. (Or are we going to call all those that occur during the neutral phase “neutral storms”? What about storms which bring disastrous flooding to California during La Niña — are we going to call them El Niño storms??) And El Niño does not make landfall, touch down or bring down a tree.
  • Abnormal or bizarre. El Niño is a natural part of our world, and has been so for many thousands of years if not millions.
  • The sole cause of individual weather events or the sole influence upon seasonal/subseasonal weather patterns. The water/land/atmosphere/sun climate system is extraordinarily complex.
  • Something that necessarily increases the amount of weather calamities. There are certain locations that do typically have increased odds of specific kinds of effects, including harmful ones, but ***plenty of extremes and disasters of all kinds occur around the world when El Niño is not present***. What El Niño does is tend to skew regional probabilities thereof by shifting weather patterns in parts of the world. It can even help bring positive effects to some places.

What El Niño *is*

Sea surface temperature (SST) departures from average January 7, 2016; NOAA/NWS/EMC
  • The term “El Niño” means the boy Christ-child, and its application in this sense originally referred to a warm current arriving each year off the coast of Peru and Ecuador during the Christmas season. Its usage was eventually narrowed to apply to particularly strong periodic warming that disrupted the local fish and bird population and extended west across the equatorial Pacific to near the dateline.
  • El Niño is an ocean phenomenon that influences the weather and short-term climate. It specifically refers to above-average sea surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean. The image above shows that pool of relatively warm water during the current exceptionally strong El Niño.
  • The opposite of El Niño below-average SSTs in that portion of the Pacific — is known as La Niña. When SSTs are near average, that is called the “neutral phase.”
  • El Niño and La Niña are related to both ocean temperature changes (on and below the surface) and the natural ebb and flow of trade winds across the tropical Pacific. The associated fluctuation in atmospheric pressure is known as the Southern Oscillation. The “coupled” oceanic-atmospheric interaction is known as ENSO (El Niño - Southern Oscillation).
  • Not only are all El Niños not the same in terms of the effects they produce, the nature of the El Niños themselves varies in terms of strength, “flavors,” and location (eastern vs. central Pacific types), including what’s known as “El Niño Modoki.”
  • The ENSO pendulum is affected by other factors, leading to irregularity in how long El Niño and La Niña last (months to multiple years), and how often they occur (every 2 to 7 years).
  • An alternative measure is known as the “Multivariate ENSO Index,” or MEI, which includes other elements such as pressure, wind, air temperature, and cloudiness.
Red peaks = El Niño; blue downward spikes = La Niña

What El Niño *does*

  • El Niño has a direct effect upon the atmosphere over/near the equatorial Pacific.
  • It has an indirect influence upon weather patterns in other parts of the world, including in and near the United States.
  • The degree of this influence depends in part on El Niño’s strength, which can vary, and on other weather and climate factors; outcomes in any given location during one El Niño as compared to another can be very different. Below are a couple of examples of that, highlighting precipitation in autumn 2015 and how it differed from previous strong El Niños. Conversely, El Niño & La Niña can produce similar outcomes.
Click on image for full-size version. Dark blue line shows seasonal precipitation-to-date October through late December 2015, compared to other strong El Niños (dimmer blue lines) and average of strong El Niños (bold light blue line). NOAA/NCEI
November precipitation departures from average in California during 5 strongest El Niños at that time of year since 1950
  • A quintessential influence of El Niño in the United States is strength and persistence of the subtropical jet stream and southern branch of the polar jet stream, especially during winter and into early spring. The yellow/orange/red shades on the map below show above-average west-to-east upper-level wind velocities with the strongest El Niños since 1950 during January-April. (There is less consistency in December.) This in turn is typically associated with storminess and above-average precipitation along the southern tier of the country.
  • Other factors can overwhelm the ENSO influence, for example a repetitive pattern (“high-latitude blocking”) over the Canada/Greenland region resulted in a lot of snow and cold weather in parts of the eastern & central U.S. in both the winter of 2009–2010 and 2010–11, despite El Niño being present in the former and La Niña in the latter.
  • Even when El Niño’s influence dominates, there can be individual exceptions within seasonal averages. For example, the winter of 1982–83 (with a very strong El Niño) was generally a mild and snowless one in the Northeast Megalopolis, but within that season, one of the most historic Northeast snowstorms occurred on February 11, 1983.


  • While El Niño can enhance the eastern Pacific season, and may have been a (but if so not the only) contributing factor to the record-shattering 2015 season throughout the Pacific, there’s a correlation between El Niño and a reduced total number of tropical storms and hurricanes in the Atlantic basin. However, the potential for disastrous impacts exists in any hurricane season including those during which El Niño is present.
  • For example, while some El Niño hurricane seasons have been relatively benign along the U.S. coast, that’s the case at times also when La Niña or the neutral phase is present, and some of the most notorious U.S. tropical cyclones on record have occurred during El Niño, including Audrey (1957), Betsy (1965), Camille (1969) and the Charley-Frances-Ivan-Jeanne barrage (2004).
  • Elsewhere this was exemplified most recently, during the 2015 hurricane season, in Dominica from Erika and the Bahamas from Joaquin. #GodzillaIsNotOmnipotent


  • Research has been published which has established some correlation between El Niño and tornado distribution (when/where), but the short-lived, highly localized, extremely capricious nature of tornadoes renders providing meaningful seasonal forecasts of the threat to any given community impossible. Prediction of tornado impacts can be challenging minutes ahead of time, and with a preciously fine line between a near-miss and catastrophe, between life and death — with or without El Niño.


  • Is El Niño’s reputation in California deserved? Only partially. Jan Null’s site has a wealth of information including about the nature of the relationship between Cali and ENSO, including this revealing table:
Period of study: 1949–1998; damage calculated in 1998 dollars

Four of those were with El Niño present, but the majority (four neutral phase, two La Niña) were not.

The author with a shirt that he couldn’t resist purchasing!

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Stu Ostro

Written by

Stu Ostro

Weather-obsessed wx geek & proud to be! Sr. meteorologist @weatherchannel. Double IPA. Quadruple espresso. Loud Music♫. @JayhawkRdrnnr.

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